What effect does a clenched fist have on the pulsatility index of the brachial artery Doppler?

The pulsatility index (PI) is a measure of the variability of blood flow and can provide insights into the resistance and compliance of blood vessels. When a fist is clenched, the muscles in the forearm and hand contract, leading to an increase in resistance to blood flow in the arteries, including the brachial artery. This increased resistance translates into a higher pulsatility index, as the Doppler signal reflects the changing velocities of blood flow during the cardiac cycle.

As the arteries are compressed, the diastolic component of blood flow may be reduced, leading to a more pronounced difference between systolic and diastolic velocities. This results in a higher PI, indicating increased resistance in the vascular bed due to the muscular contraction caused by clenching the fist. Thus, the act of making a fist directly correlates to an increase in the pulsatility index of the brachial artery.

In contrast, the other options do not account for the physiological changes that occur during muscle contraction in relation to vascular resistance.